Magnetic phonograph pickup having plural inducing magnets

ABSTRACT

A magnetic phonograph pickup comprises interfitting stylus and sensing assemblies. The stylus is connected to a ferromagnetic element which is magnetically saturated by at least a pair of permanent magnets which are arranged, in a common plane at right angles to the plane of symmetry through the stylus assembly, adjacent this element with similar poles directed toward it. The sensing arrangement comprises coils adjacent the element which sense its movement and produce an output signal. The entire pickup is symmetrical about a central plane of symmetry, and the magnets are inclined to this plane.

United States Patent Westerkamp et al. Feb. 8; 1972 [54] MAGNETICPHONOGRAPH PICKUP [56] References Cited g gg g INDUCING UNITED STATESPATENTS 3,441,688 41969 Sh ..l79 100.4l K [72] Inventors: l-lugoWesterkamp, Prechtal, Germany; 3 294 405 1211966 iggg 274/37 v RobertDubois Colombiar Switzerland 3,538,266 ll/l970 Cho l79/l00.41 K [73]Assignee: Huber 8: Co., Hautervie, Switzerland I Primary ExaminerStanleyM. Urynowicz, Jr. Filed 1969 Assistant Examiner-Raymond F. Cardillo, Jr.[21] Appl. No.: 885,391

[57] ABSTRACT [30] Foreign Application Priority Data A magneticphonograph pickup comprises interfitting stylus D e c 16 1968Switzerland 1871 8/68 and sensing assemblies. The stylus is connected toa ferromag- 1969 Switzerland "16922/69 nefic element which ismagnetically saturated by at least a pair of permanent magnets which arearranged, in a common plane 52] US. Cl. ..179/100.41K, 274/37 at rightangles the Plane symmetry thmhgh the Stylus 51 lm. Cl .1104: 11/12Semhly, adjacent this element Whh Similar Poles directed [58] Field ofSearch ..179/100.41 A, 100.41 s, 100.41z; toward The Sensing arrangementcomprises eeils adjacent 274/37 the element which sense its movement andproduce an output signal. The entire pickup is symmetrical about acentral plane of symmetry, and the magnets are inclined to this plane.

10 Claims, 18 Drawing Figures PAIENIED EB 8 2 SHEET 3 [IF 4 Fig.10

MAGNETIC PHONOGRAPI'I PICKUP HAVING PLURAL INDUCING MAGNETS l. FIELD OFTHE INVENTION The present invention relates to a magnetic phonographpickup and, more particularly, to such a pickup for use withstereophonical phonograph recordings. 7

2. BACKGROUND OF THE INVENTION A magnetic pickup or cartridge generallycomprises a stylus which resiliently is carried by the pickup housingand is substantially rigidly connected to an element which is either apermanent magnet itself or in which a flux is induced by a permanentmagnet mounted in the pickup. As the stylus or needle vibrates oroscillates because of variations in the record groove corresponding tothe recording thereon, coils adjacent the magnetically permeable movableelement of the stylus detect the variations in the flux therethrough andproduce an output signal corresponding to variations in the flanks orroot of the groove.

In the case of a stereophonic recording each flank of a usuallyright-angle groove carries one channel and the movement of the elementin two mutually perpendicular planes is separately sensed byrespectivesets of coils.

Such a pickup or cartridge is often bulky and relatively insensitive tominute variations in the groove, while being open to influence fromexternal magnetic sources. Furthermore, the power output of such apickup is often insufficient for many amplifiers, and must be fedthrough a costly preamplifier for use. Also, to achieve high poweroutputs, large cartridges have been necessary, thereby increasing thetracking weight of the pickup arm, increasing wear of the record,reducing sensitivity to minute changes of the track, and increasing wearof the jeweled tip or point of the stylus assembly.

It is, therefore, an object of the present invention to provide animproved magnetic phonograph pickup.

Another object is to provide such a pickup which is highly sensitive,which produces a relatively strong and distortionfree output, and whichis relatively insensitive to outside magnetic fields.

3. SUMMARY OF THE INVENTION The above objects are attained, inaccordance with the present invention, by a pickup or cartridge of theabovedescribed type wherein at least two coplanar magnets are mountedadjacent the'element, with similar poles directed at this element. Inthis manner the element is subjected to a relatively strong field whichcan be sensed by the coils of the pickup. These magnets are preferablypermanent magnets which are each lined up with the element, that is,whose north poles are turned away from the element while their southpoles are turned toward this element, or vice versa. The use of two ormore magnets arrayed around the element creates a field which isconcentrated in the element to a much larger extent than would bepossible with a single, large magnet.

According to another feature of the present invention, the entire pickupis symmetrical about a median plane of the stylus and the element, withone magnet to each side of this plane. Another feature of the inventionprovides for arraying the magnets, each with an inclination at about 30to the symmetry plane.

A pickup so constructed can produce a large output while havingrelatively low weight. Since the field is concentrated in the littleelement to a much higher degree than otherwise possible, this elementand the stylus can be of lighter weight than heretofore and yet canproduce an output corresponding to the minimum standards of the industryor better. Of course, the smaller the pickup, the more sensitive it is.Furthermore, the concentrated field is so strong that any outside fieldswill have no effect on it, since these outside fields will be relativelyweak.

The above and other objects,features, and advantages will becomeapparent from the following description, reference being made to theaccompanying drawing, in which:

LII

FIG. 1 is a perspective view of the stylus assembly of a firstembodiment of the present invention, partly broken away;

FIG. 2 is a perspective view of the sensing arrangement of the firstembodiment of the present invention;

FIG. 3 is a schematic diagram of the sensing arrangement of the firstembodiment of the present invention shown in FIG. 2;

FIG. 4 is a top view, partly in section, of the needle assembly of thefirst embodiment of the present invention;

FIG. 5 is an end view, taken in the direction of arrow V of FIG. 4 ofthe first embodiment of the invention;

FIG. 6 is a cross section through a second embodiment of the presentinvention corresponding roughly to a section taken through line VI-VI ofFIG. 4;

FIG. 7 is a top view, partly in section, of a third embodiment of thepresent invention;

FIG. 8 is an end view taken in the direction of arrow VIII of FIG. 7 ofthe third embodiment of the present invention;

FIG. 9 is a longitudinal section through a fourth embodiment of thepresent invention;

FIG. 10 is an end view of the fourth embodiment shown in FIG. 9;

FIGS. 11 and 12 are details of FIGS. 9 and 10, respectively, in enlargedscale;

FIGS. 13 and 14 are views corresponding to FIGS. 11 and 12,respectively, showing a fifth embodiment of the present invention; and

FIGS. 15, 16, 17, and 18 are views corresponding to FIGS. 9, 10, 11, and12, respectively, showing a sixth embodiment of the present invention.

THE EMBODIMENTS OF FIGS. 1-5

A pickup comprises a needle or stylus assembly formed by a solid block 2of synthetic resin in which is embedded a pair of magnets 3 with theirnorth poles turned inwardly and south poles outwardly. The block 2 isnotched out at 4 between the two north poles, with the base 5 of thenotch 4 being V-shaped and having an apex lying in and defining a planeS of symmetry. Fitted into the back of the block 2 is a brass sleeve 6of square cross section which is rigidly held in the block and extendsalong the plane S. The magnets 3 lie symmetrically on opposite sides ofthe symmetry plane S and have faces exposed at the notch 4.

An annular resilient rubber washer 7 having a square outline but a roundcenter hole is snugly received in the tube 6 just behind the block 2 andin turn receives and resiliently mounts a ferromagnetic element 8 in theform of a short cylindrical sleeve having a diameter equal to about halfthe width of the tube 6 and a length equal to about a third that of thetube 6 and block 2 together along the plane S of symmetry. Asubstantially S-shaped aluminum tube 9 is fitted into the end of theelement 8 extending into the block 2 and has a flattened end 10 whichextends beyond the block 1 and carries a small diamond or sapphirestylus 1 1. A small nonmagnetic wire 12 is soldered to both the tube 8and sleeve 6 to prevent them from being displaced axially relative toeach other and to hold the element 8 parallel to the tube 6 when thehead of the tone arm holding the pickup is resting on a record.

The pickup also comprises a sensing arrangement 13 having a pair ofsubstantially U-shaped magnetic bands 14 and 15 forming a pair of poles16 and 17 and each wrapped by a coil 18 or 19. This unit 13 (see FIGS. 2and 3) is held in an openended housing 20 forming a magnetic return pathwhile permitting insertion of the needle assembly (and arrangement 13 inits open end). These poles 16 and 17 lie in mutually perpendicularplanes flanking the symmetry plane S. Similar to the tube 6 of squarecross section, the poles l6 and 17 define a square whose diagonal lieson the plane S of symmetry. These poles 16 and 17, in the assembledpickup, lie just adjacent the brass tube 8.

As the stylus 11 rides in a groove of a stereophonic recording, it isdisplaced with components of displacement in two separate mutuallyperpendicular planes by the variations cut into each flank of thegroove. Each flank of this groove corresponds to one stereophonicchannel and lies generally at 45 to the symmetry plane S. Thus, theelement 8 moves in two planes along with the stylus, the resilientwasher 7 allowing a slight conical movement of this element 8. Sinceboth north poles of the magnets 3 are directed at the element 3 and thestrength of these magnets is sufficient to saturate the element 3, themagnetic field in it also gyrates and generates a varying output voltagein the coils 18 and 19. The magnetic effect of the two magnets 3 in theelement 8 is much greater than that which would be produced by a singlemagnet, even if it were larger than either of the magnets 3, so that thefield is stronger and easier to sense. It follows that the element 8 andother parts of the pickup 1 can be much smaller than customary, yetdeliver a more than adequate output, in such a manner that a lighter,more sensitive pickup is produced.

The usual desirable voltage output for a magnetic pickup having a stylusvelocity of 1 cm./sec. and a load of around 47,000 ohms is between about0.5 and 1.0 millivolts. The entire weight of the stylus assembly can begreatly reduced according to the present invention while still producingthis above-described output. Of course, the lighter the stylus is, themore sensitive the pickup is. At the same time, the relatively intensemagnetic field passing through the element 8 and housing 20 is lesssensitive to outside magnetic fields.

THE EMBODIMENT OF FIG. 6

A needle holder la has a synthetic-resin base 2a which is identical tothat of FIGS. l-S in every way except that it mounts a third magnet 3awhich lies in the plane of symmetry S. The two magnets 3 lie in a commonplane perpendicular to the plane of symmetry, as in FIGS. 15. In such anarrange ment the strength of this third magnet is so chosen that theelement 8 is just saturated. Three very small magnets here have theeffect of a very large one, all with their north poles lying very nearthe element 8.

THE EMBODIMENT OF FIGS. 7 AND 8 A needle holder lb has a synthetic-resinblack 2b in which are mounted two long magnets 3b of square crosssection. These magnets 3b are arranged with their axes A at an angle ofaround 30 to the plane of symmetry of the pickup. The stylus 11 ismounted in an aluminum tube 9b which has an end 24 press fitted into aferromagnetic element 8b formed by two parallel ferromagnetic strips 25.The magnets 3b include an angle of 60 with one another.

In this embodiment the elongated magnets 3b both have their south polesturned toward the element 8b and their north poles extending to the edgeof the block 2b. Such a construction very exactly focuses the lines offorce of the magnets 3b on the element 817 while the outer ends are wellarranged for the path of the magnetic field. In all other respects, thisembodiment is identical to that of FIGS. l-S.

THE EMBODIMENT OF FIGS. 9-12 A pickup cartridge has a removable needleassembly 1c formed by a block 2c in which are mounted two magnets 30extending perpendicularly to the symmetry plane S with their south polesturned toward the element 8 which, with the stylus l l and tube 6 isessentially identical to that of FIG. 1.

The pickup further comprises a housing 26 formed by a pair of plasticmembers 27 and 28 which are held together by pins 29. Holes 30 areprovided in the wide underportion 28 of the housing 26 to allow theentire assembly to be mounted in a tone arm by a pair of screws.

The sensing means includes four parallel magnetic core pieces 31defining four poles 32 and each provided with a coil 33. Diagonallyopposite coil 33 are connected in series and thence to connecting pins35 fixed on a synthetic-resin element 34. These sensing coils 33function essentially the same as the coils of FIGS. 1-5.

The needle assembly 1c has a brass tube or sleeve 36 which is onlyslightly longer than the element 8 of FIGS. 15,

although in all other respects this assembly 1c is virtually identicalwith that of FIGS. 1-5. The magnets 3c each have a beveled corneradjacent the element 8 but their upper surfaces lie parallel to a line Lthrough the center of this element- 8. As in FIGS. 1-5, 7, and 8 themagnets lie in a plane perpendicular to the symmetry plane S, that is,with their north and south poles in line behind each other andorthogonal to this plane.

THE EMBODIMENT OF FIGS. 13 AND 14 There is shown here a needle assembly10 having asynthetic-resin block 2d in which are mounted a pair of smallelongated magnets 3d. Each magnet 3d defines an axis A directed at theelement 8 and extending at an angle of 30 to the symmetry plane S and ata similar angle to a plane P perpendicular to this plane S and to theelement 8. The assembly 1d like all the other embodiments, remains fullysymmetrical, with the magnets 3d advantageously directed toward theelement 8. In all other respects this embodiment is identical to that ofFIGS. 9l2.

THE EMBODIMENT OF FIGS. 1518 A pickup has a housing 37 formed by a topelement 27' and a base 38, the latter being essentially identical to thebase 28 of FIGS. 9 and 10, as are the coils 31-33 and the connections Aneedle assembly 1e is provided which is substantially lighter than thatof any of the other embodiments, and substantially less expensive tomanufacture, as will be seen below. This assembly is identical to thatof FIGS. 9-12, except that it has a synthetic-resin base 2e in which areembedded a pair of ferromagnetic cylinders 39 defining axes A".

Mounted in the blocks 27 and 38 are a pair of cylindrica magnets 3elying on the axes A which extend at around 30 to the symmetry plane 5and form a slightly acute angle with the element 8. The cylinders 39serve as pole pieces to focus the south poles of the magnets 3e on theelement 8.

Such a pickup is especially advantageous since the needle assembly,which is held in place by resilient clips, does not include the magnets,but only has a pair of small ferromagnetic cylinders. Thus, thisassembly, which is the only part of the pickup prone to wear and oftenin need of replacement, is simple and inexpensive to manufacture.

What is claimed is:

l. A magnetic phonograph pickup comprising:

a pickup housing;

a stylus resiliently carried by said housing;

a ferromagnetic element operatively connected with said stylus for jointmovement therewith;

magnetic means including at least two magnets mounted on said housingadjacent said element and on opposite sides thereof, said magnets havingsimilar magnetic poles turned toward said element, all of the magnets ofsaid magnetic means being disposed adjacent said element and having fluxpaths passing directly through said element while being the solemagnetized bodies in said housing; and

coil means mounted on said housing adjacent said element for excitationby a magnetic field induced in said element by said magnets.

2. The pickup defined in claim 1 wherein said magnets are coplanar andare arrayed symmetrically with respect to a plane of symmetry passingthrough said element and said stylus.

3. The pickup defined in claim 2 wherein said magnets lie substantiallyperpendicular to said plane of symmetry.

4. The pickup defined in claim 2, further comprising a third magnetadjacent said element and having a pole similar to said magnetic polesof the first mentioned magnets turned toward said element, said thirdmagnet lying along said plane.

5. The pickup defined in claim 2 wherein said magnets are inclined tosaid plane.

6 The pickup defined in claim 5 wherein said magnets are elongated andinclude angles of about 30 with said plane.

7. The pickup defined in claim 1 wherein said element is a ferromagnetictube.

8. The pickup defined in claim 7 wherein said housing comprises anonmagnetic sleeve and a resilient washer therein, said tube beingresiliently mounted in said washer.

9. The pickup defined in claim 1, wherein said housing com- I prises apair of interfitting synthetic-resin blocks, said stylus

1. A magnetic phonograph pickup comprising: a pickup housing; a stylusresiliently carried by said housing; a ferromagnetic element operativelyconnected with said stylus for joint movement therewith; magnetic meansincluding at least two magnets mounteD on said housing adjacent saidelement and on opposite sides thereof, said magnets having similarmagnetic poles turned toward said element, all of the magnets of saidmagnetic means being disposed adjacent said element and having fluxpaths passing directly through said element while being the solemagnetized bodies in said housing; and coil means mounted on saidhousing adjacent said element for excitation by a magnetic field inducedin said element by said magnets.
 2. The pickup defined in claim 1wherein said magnets are coplanar and are arrayed symmetrically withrespect to a plane of symmetry passing through said element and saidstylus.
 3. The pickup defined in claim 2 wherein said magnets liesubstantially perpendicular to said plane of symmetry.
 4. The pickupdefined in claim 2, further comprising a third magnet adjacent saidelement and having a pole similar to said magnetic poles of the firstmentioned magnets turned toward said element, said third magnet lyingalong said plane.
 5. The pickup defined in claim 2 wherein said magnetsare inclined to said plane.
 6. The pickup defined in claim 5 whereinsaid magnets are elongated and include angles of about 30* with saidplane.
 7. The pickup defined in claim 1 wherein said element is aferromagnetic tube.
 8. The pickup defined in claim 7 wherein saidhousing comprises a nonmagnetic sleeve and a resilient washer therein,said tube being resiliently mounted in said washer.
 9. The pickupdefined in claim 1, wherein said housing comprises a pair ofinterfitting synthetic-resin blocks, said stylus being resilientlycarried by one of said blocks, said pickup further comprising at leasttwo elongated metallic bodies extending from said poles of said magnetsto immediately adjacent said element.
 10. The pickup defined in claim 1wherein said element comprises a pair of substantially parallelferromagnetic strips coupled with said stylus.